The invention pertains to a transport system and to a method for controlling the transport system. Such transport systems are used in the fabrication of wafers in the semiconductor field and they are an essential part of the production and automation concept.
Conventional transport systems, which are known as trolley systems, for example, have numerous disadvantages. One of the more significant disadvantages of the prior art systems resides in the fact that it is possible to expand or change the transport paths only with a high outlay, and that the control operates in a manner that is quite susceptible to faults. These disadvantages may be ascribed, inter alia, to the fact that a superordinate control unit is responsible for all the data that arise, and that the transport system is provided with too few control points which could enable monitoring of the individual trolleys. In the event of a fault, fault propagation occurs and can lead to a failure of the complete transport system and an attendant breakdown on account of the small number of control points and on account of the extensive system communication which has to be processed by a superordinate control unit.
It is accordingly an object of the invention to provide a transport system and a control method for controlling the transport system, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which ensures the robustness of the system and the remainder of the system continues to operate in a dependable manner even in the event of a fault or the failure of individual components.
With the foregoing and other objects in view there is provided, in accordance with the invention, a transport system for transporting a multiplicity of individual items, comprising:
a multiplicity of conveying devices for transporting individual items;
a multiplicity of branching devices connected to respective conveying devices for selectively branching the items to different conveying devices;
a multiplicity of processing devices for processing the items, the processing devices having inlets and outlets connected to respective conveying devices;
a multiplicity of storage devices for temporarily storing the items;
an information medium attached to each item for storing at least one first destination address identifying a specific processing device to which the respective item is to be transported;
a writing device at each outlet of a respective processing device for writing a second destination address after a processing operation and upon transferring the item to a respective conveying device; and
each branching device reading the information medium of each item and utilizing an internal destination address list to define a branching direction for the respective item.
In other words, the transport system is used in particular to transport wafers and it comprises a multiplicity of carrier devices which accommodate the wafers, a multiplicity of conveying devices, which transport the carrier devices, a multiplicity of branching devices, which branch the carrier devices to different conveying devices, a multiplicity of inlets and outlets (lifts) at processing devices, at which the wafers are processed, and a multiplicity of storage devices, in which the carrier devices with the wafers are temporarily stored. Each carrier device has an information medium, in which at least one first destination address is stored, with the result that the associated wafers can be transported to a specific processing device corresponding to this destination address. The first destination address is read at each lift at a processing device, and a second destination address is written after the processing operation by the lift, and each branching device uses an internal destination address list to define the branching direction in that the information medium of each carrier device is read at each branching device.
In accordance with an added feature of the invention, the second destination address corresponds to a production area, the item to be transported being processed at the first destination address and then transported to a first storage device of this production area.
In accordance with an additional feature of the invention, if the first storage device of this production area is occupied, the item to be transported successively selects all the other storage devices of this production area until a free storage location is reached.
These features serve the purpose of independent control. The transport organization is thus executed at a lowest control level of the transport system.
In accordance with another feature of the invention, the item is transported in a circle in the afore-mentioned production area if all the storage devices are occupied. This has the effect that the conveying devices themselves are used as temporary stores for the items.
In accordance with a further feature of the invention, the destination address lists in each branching device are set up in a specific manner and include all the destinations which can be reached via the specific branching device. In accordance with again a further feature of the invention, the destination address lists include only the destinations which cannot be reached in a preferred direction of the branching device. This results in optimization of the address lists so that, on the one hand, their size is kept small and, on the other hand, alternative routes can nevertheless be traveled.
In accordance with again an added feature of the invention, a further improvement in route planning is afforded where each branching device additionally takes account of the activities of neighboring branching devices when the branching direction is determined, in order to optimize the transporting path. In analogy to traffic control, transport paths which are already severely loaded can be circumvented.
In accordance with again an additional feature of the invention, the content of the information medium on the item is nonvolatile. The destination addresses are thus retained and the transport task can be resumed even after a power failure.
In order to be able to react suitably to exceptional situations, according to again another feature, the transport system comprises additional address lists in each branching device, which address lists can be activated in exceptional situations, such as fire alarm, deactivation of the transport system and partial deactivations of the transport system. Furthermore, the destination address lists and the additional address lists may be continuously updated in order constantly to register changes in the set-up of the transport system.
Transport reliability may be further improved, in accordance with additional features of the invention, which ensure that transport tasks which are en route for an exceptionally long time are ascertained, in which case a transport task is begun by removal of the item from the storage device, the destination addresses are written to the information medium of that item, the item is transported by means of the conveying devices and is branched in the direction of the first destination address by means of the branching devices, processing being carried out after the processing device corresponding to the first destination address has been reached, and then the item is provided with the second destination address in order to be transported further. If the time interval between removal from storage and processing is longer than a predetermined time period, the item is placed onto a fault list.
In order to unambiguously identify the item to be transported, each item is allocated a specific number which is likewise stored in the information medium, this number being entered in the above-mentioned fault list.
With the above and other objects in view there is also provided, in accordance with the invention, a method of controlling a transport system which comprises the following steps:
removing an item to be transported from a storage device;
storing at least a first destination address in an information medium of the item;
transporting the item along a multiplicity of conveying devices;
reading-out the destination address from the information medium of the item at one of a multiplicity of branching devices disposed between the conveying devices;
comparing the destination address obtained in the reading-out step with an internal destination address list in the branching device;
setting a branching direction of the branching device depending on a result obtained in the comparing step, and branching the item in a direction towards the first destination address;
repeating the transporting, reading-out, comparing, and setting steps until a processing device corresponding to the destination address has been reached;
processing the item in the processing device;
storing and/or reading a second destination address at the information medium of the item, and transporting the item further towards the second destination address.
In other words, the transport control process is characterized by the following: Removal of an item to be transported from a storage device, storage of at least one first destination address in the information medium, transporting of the item by means of a multiplicity of conveying devices, wherein the branching devices branch the item to different conveying devices, read-out of the destination address from the information medium of the item at each branching device, comparison of the destination address which has been read with an internal destination address list in the branching device, setting of the branching direction of the branching device depending on the result of this comparison, and branching the item towards the first destination address, repetition of the steps transporting/read-out/comparison/setting until a processing device corresponding to the destination address is reached, processing of the product, storage and/or reading of a second destination address in and/or from the information medium in order to transport the item onward to a further production area.
In accordance with yet an added feature of the invention, the respective internal destination address lists include all the destinations which can be reached via the branching devices. This leads to the optimization of the transporting paths and makes possible alternative routing of the items.
In order to minimize communication in the system, it is possible, in accordance with yet an additional feature of the invention, for a second destination address to be written together with the first destination address to the information medium during the removal from storage operation, and for the first destination address then to be replaced or overwritten by the second destination address after the processing operation.
According to the fundamental concept of the present invention, namely that of realizing decentralized transport control at a lowest control level, the branching device uses the internal destination address list to determine the branching direction, independently of a superordinate control device. In accordance with yet a further feature of the invention, therefore, the superordinate control device updates the destination address list in the branching devices when the configuration (expansion, alteration, partial or complete deactivation of transporting paths, additional branching devices, etc.) of the transport system changes.
In accordance with a concomitant feature of the invention, further address lists are stored in the branching devices in addition to the internal destination address lists, and can be activated in exceptional cases, such as, for example, fire alarm or (partial) deactivation of the transport system.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a transport system and method for controlling the transport system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing FIGURE.